1. Field of the Invention
The present invention relates to a speed control circuit of a direct current motor for a battery-operated type electric powered tool.
2. Description of the Related Art
In a charging type electric powered tool, in the case of changing a motor speed in accordance with a dial setting value, a speed control circuit is mounted in the electric powered tool. By using an already existing IC (Integrated Circuit) as much as possible, it is possible to readily manufacture the speed control circuit.
However, an IC designed for only speed control circuit of a direct current motor is constructed as an IC for a servo motor used for position control, which detects a rotational speed of a motor so as to carry out a speed control with the use of an encoder or the like. For this reason, in the case where the aforesaid IC has been applied to an electric powered tool which roughly increases and decreases the rotational speed, the IC includes many functions which are not used; therefore, it is very expensive to apply the aforesaid IC to the electric powered tool Thus, a speed control circuit of the electric powered tool is constructed in a manner of combining a plurality of general ICs Including an operational amplifier or the like; as a result, it is impossible to cheaply and readily manufacture the speed control circuit of the electric powered tool.
The present invention has been made in order to solve the aforesaid problem in the prior art. It is, therefore, an object of the present invention is to provide a speed control circuit of a direct current motor for an electric powered tool, which is capable of being readily constructed.
A speed control circuit of a direct current motor, which applies a voltage of battery so as to control a rotational speed of a direct current motor of an electric powered tool according to the present invention, comprising:
a switching regulator IC generating a variable potential in accordance with a command potential;
an electrically energizing control element connected to an output side of said switching regulator IC, and turning on and off a current to said direct current motor from said battery; and
a command potential applying device connected to an input side of said switching regulator IC, and applying a potential corresponding to a (dial) setting value.
According to the present invention, a general switching regulator IC is used to construct a speed control circuit of the direct current motor; therefore, it is possible to cheaply and readily manufacture the speed control circuit of the direct current motor. Further, the switching regulator IC has a wide source (supply) voltage range; therefore, there is an advantage of separately requiring no step-down power circuit even if a higher voltage battery is used.
According to a preferred embodiment of the present invention, the speed control circuit of a direct current motor, said switching regulator IC includes:
a reference voltage generator generating a reference voltage:
a first operational amplifier making a comparison between a potential from said reference voltage generator and a potential from said command potential applying device;
a triangular wave generator; and
a second operational amplifier making a comparison between a triangular wave from said triangular wave generator and an output from said first operational amplifier, and outputting a control signal to said electrically energizing control element. It is possible to use the whole functions of the switching regulator IC without wasting any section.
A speed control circuit of a direct current motor, which applies a voltage of battery so as to control a rotational speed of a direct current motor of an electric powered tool according to the present invention, comprising:
a switching regulator IC generating a variable potential in accordance with a first command potential applied to a first input and a second command potential applied to a second input;
an electrically energizing control element connected to an output side of said switching regulator IC and turning on and off a current to said direct current motor from said battery;
a first command potential applying device applying a potential corresponding to a (dial) setting value to said first input side; and
a second command potential applying device applying a potential corresponding to a pulled position of a trigger of electric powered tool to said second input side.
Moreover, according to the present invention, a general switching regulator IC is used to construct a speed control circuit of the direct current motor; therefore, it is possible to cheaply and readily manufacture the speed control circuit of the direct current motor. A switching regulator IC, which generates a variable potential in accordance with a first command potential applied to a first input and a second command potential applied to a second input, is used; for this reason, a potential corresponding to a dial setting value of a first command potential applying device is applied to the first input side, and thereby, a speed of the motor can be adjusted in accordance with the setting value of the dial. Further, a potential corresponding to a pulled position of a trigger of the electric powered tool is applied to the second input side, and thereby, a speed of the motor can be adjusted in accordance with the pulled position of the trigger. Also, the switching regulator IC has a wide source (supply) voltage range; therefore, there is an advantage of separately requiring no step-down power circuit even if a higher voltage battery is used.
According to a preferred embodiment of the present invention, the speed control circuit of a direct current motor, said switching regulator IC includes:
a reference voltage generator generating a reference voltage;
a first operational amplifier making a comparison between a potential from said reference voltage generator and a potential from said first input;
a third operational amplifier making a comparison between a potential from said reference voltage generator and a potential from said second input;
a triangular wave generator; and
a second operational amplifier making a comparison between a triangular wave from said triangular wave generator and outputs from said first operational amplifier and said third operational amplifier, and outputting a control signal to said electrically energizing control element. It is possible to use all the functions of the switching regulator IC.
According to the preferred embodiment of the present invention, in the switching regulator IC, a second operational amplifier outputs a control signal to an electrically energizing control element on the basis of a potential value on a lower side of which a potential from a first operational amplifier or a potential from a third operational amplifier Thus, a motor speed can be adjusted in accordance with a pulled position of the trigger in a range of dial set in the first command potential applying device.